Method of and apparatus for imparting an electrical charge to a web of film or paper or the like

ABSTRACT

An electrical charge is applied to a moving web of flexible material such as film or paper by transporting the web over a grounded roller while maintaining a stationary electrically charged plate adjacent to the web but spaced slightly therefrom. A direct current voltage of the required sign and magnitude is applied to the plate from any suitable source such as a generator or battery. Alternatively the plate can be grounded and the voltage applied to the roller.

United States Patent Whitmore, Jr. et al.

[54] METHOD OF AND APPARATUS FOR IMPARTING AN ELECTRICAL CHARGE TO A WEBOF FILM OR PAPER OR THE LIKE [72] lnventors: Thomas C. Whltmore, Jr.,Rochester; Robert G. Cunningham, Pittsford, both of [73] Assignee:Eastman Kodak Company, Rochester,

[22] Filed: April 20, 1970 [21] App]. No.: 29,816

[52] U.S. Cl ..317/2 R, 317/262 A [51] Int. Cl. ..H05f 3/00 [58] Fieldof Search ..3l7/262, 2; 18/1 FZ; 324/32;

250/49.5 TC, 49.5 GC; 118/620, 621

[56] References Cited UNITED STATES PATENTS 2,562,138 4/1950 Bump et al.,3l7/2 X [151 3,670,203 June 13, 1972 3,164,747 1/1965 Yahnke ..317/23,396,917 8/1968 Carter ..3l7/2 X 3,503,526 3/1970 Crafton.........3l7/2 X 3,536,528 10/1970 De Geest ..317/262 A 3,196,063 7/1965Paquin et al. ..317/262 A 2,879,396 3/1959 McDonald .317/262 A X3,405,052 10/1968 Schirmer ..250/49.5 X

Primary Examiner-L. T. Hix Assistant Examiner-Harry E. Moose, Jr.Attorney-Walter O. Hodsdon and Henry M. Chapin [57] ABSTRACT Anelectrical charge is applied to a moving web of flexible material suchas film or paper by transporting the web over a grounded roller whilemaintaining a stationary electrically charged plate adjacent to the webbut spaced slightly therefrom. A direct current voltage of the requiredsign and magnitude is applied to the plate from any suitable source suchas a generator or battery. Alternatively the plate can be grounded andthe voltage applied to the roller.

7 4 Claims, 2 Drawing Figures PATENTEnJnmmn 3.670.203

THOMAS C WH/TMOREMR. ROBERT 6. CUNNINGHAM INVENTORS Ewe/4M METHOD OF ANDAPPARATUS FOR IMPARTING AN ELECTRICAL CHARGE TO A WEB OF FILM OR PAPEROR THE LIKE BACKGROUND OF THE INVENTION 1. Field of the Invention Thepresent invention relates to a method and apparatus for applying anelectrical charge to a moving web of flexible material such as acontinuous web of photographic paper or film.

In the manufacture of such webs, they are passed between and overrollers, or through other devices, which generate electrostatic chargeson the moving webs. When such a charged web is brought near a groundedobject, sparking may occur which will be harmful to the web. Forexample, if the web has already been coated with sensitized emulsions,the spark may cause localized exposure of the emulsion. Also, sparksoccuring in a dark room will expose much more material than theimmediate piece being operated on. Furthermore, when such sparks occuron subbed photographic webs which have not yet been coated withemulsion, they may burn the subbing layers so that the emulsion will notgo on properly at a subsequent point in processing. Also, staticelectricity may be present in the form of islands of charge which willcause skips when the web is subsequently coated with emulsion. Staticcharges also may cause the attraction and accumulation of dust on thewebs, which will be detrimental to quality.

2. The Prior Art In British Pat. No. 976,027 there is describedapparatus for applying a charge to a web by passing the web over agrounded roller while applying a voltage to the opposite side of the webthrough conductive bristles of nylon, brass, or the like which are inbrushing engagement with the web. While this apparatus is operable, ithas the disadvantage of possibly scratching the web, and of depositingparticles from the bristles onto the web. Additionally, the bristles mayattract and hold particles of dirt which may be deposited on the web.Another disadvantage 'is that if the web breaks or runs out, directcontact can occur between the bristles and the grounded roller, with theformation of sparks which are particularly detrimental when photographicfilm or paper is being processed in'a darkroom.

In our pending US. Pat. application Ser. No. 3,434 which was filed Jan.16, 1970, entitled Method Of And Apparatus For Applying An ElectricalCharge To A Moving Sheet Of Flexible Material," abandoned, andcontinuation-in-part application Ser. No. 91,342, filed Mar. 1 l, l97lsame title there is described apparatus for neutralizing a staticelectric charge, or for applying a desired charge, wherein a web passesbetween two connecting rollers, one of which is connected to ground andthe other of which is connected to a source of direct current voltagefor applying a charge of desired sign and magnitude to the web. Thelatter roller is preferably covered with a semi-conductive materialwhich is sufficiently conductive for charge application, but which willnot generate sparks if the two rollers come together when a web breaksor runs out. One-of the covering materials for this roller is a plushfabric which has been treated with a surfactant to make it partiallyconductive. Our apparatus has proved to operate very effectively withoutscratching a web and without generating sparks. However, the plushfabric is apt to become contaminated with dust, or with othercontaminants which may be imparted to the web. Such contamination isparticularly disadvantageous when processing photographic film or paperthrough some steps in the production process, such as emulsion coatingoperations.

SUMMARY OF THE INVENTION The problems set forth above are solved by ourpresent method comprising applying an electrical charge to a moving webof a material such as photographic paper or film by transporting the webover a first electrically conductive body in the form of a rotatingroller while maintaining adjacent to the web on the side thereofopposite the roller a second electrically conductive body in the form ofa plate or shoe which is spaced slightly from the surface of the web,such as between I and 15 millimeters therefrom.

One of the electrically conductive bodies is connected to ground and theother is connected to a source of a direct cur rent voltage ofsufficient magnitude to pass across the gap between the web and thesecond conductive member but without developing a corona discharge. Thevoltage should be of such magnitude and sign as to develop a desiredelectrical charge condition on the web, for example, neutral, orpositively or negatively charged.

We have found it particularly desirable for an operator to determine themagnitude and sign of the static electrical charge on a web, and then toapply a voltage of the same sign and sufficient magnitude so as toneutralize the static charge, thus avoiding sparking when the web issubsequently brought near a grounded object.

In another mode of operation, a web can be precharged to a selectedvoltage by our method at one station in a production line, andsubsequently, after intermediate processing steps, can again be treatedby our method to neutralize the charge on the sheet which may or may nothave picked up additional charge.

The apparatus for performing the method described above will bedescribed in detail hereinafter.

THE DRAWINGS In the Drawings:

FIG. 1 is a schematic side elevational view showing one form ofapparatus for developing a desired electrical charge condition on a longcontinuous web of flexible material, such as photographic film or paperwhich is bent around a roller; and

FIG. 2 is a schematic side elevational view showing a modified form ofapparatus for treating a web moving in a straight line.

THE PREFERRED EMBODIMENTS Referring to FIG. 1 of the drawings, a longcontinuous web 11 of photographic film or paper is transportedcontinuously in contact with an electrically conductive roller 13 whichis connected to ground. An electrically conductive shoe or plate 15 ofarcuate shape (coinciding with the curvature of the web 11 and thesurface of roller 13) and of sufficient width to extend across web 11,is maintained in position on the opposite side of web 11 from roller 13and is spaced slightly from the web to form a gap 16 which may vary fromI to 15 millimeters so that the shoe is never in contact with the web.Shoe 15 and roller 13 can be made of an electrically conductive materialsuch as brass or other metal; or may be made of a normallynon-conductive material such as synthetic resin which has been madeconductive by impregnation with a surfactant such as asodium salt of analkylaryl polyether sulfonate, or coated with a metal such as silver. Asuitable variable power supply or source 19 of a direct current voltageis connected to the shoe 15 and is provided with voltage sign andmagnitude adjusters 21 and 23 for applying the correct voltage to theshoe. Any source can be employed, such as batteries, or a DC. generator,or a rectifier connected to an A.C. power line.

To reduce the charge on the web toward neutral, or to reverse thepolarity of the charge, the voltage applied to the shoe 15 should havethe same sign as the charge on the web; to increase charge on the webwithout changing its sign, the voltage applied to the shoe should havethe opposite sign. (The change in potential on the web is of oppositesign to the potential applied to the shoe.)

While the correct voltage to apply can be empirically determined, weprefer to position an electrostatic field meter 25 adjacent to the web11 after it has passed shoe 15, so as to continuously measure or monitorthe electrostatic field resulting from any electrical charge on the web,and to display it on a meter 27. The operator observes the voltage andits sign on the meter 27, and adjusts the voltage supply 19 as needed soas to assure the correct charge and sign. An electrostatic field metersuitable for this purpose is described in the July, 1950 issue of theJournal of the Society of Motion Picture and Television Engineers" in anarticle by H.W. Cleveland on pages 37-44 entitled, A Method of MeasuringElectrification of Motion Picture Film Applied to Cleaning Operations."

The charge which has built up on a web 11 of photographic material maybe quite large, resulting in electrostatic potentials of anywhere from100 to 50,000 volts. The charge may have a positive or negative sign,depending upon the nature of the web material, and of the rollers orother apparatus through or over which it has been passing. Thus, toneutralize, it is necessary to apply a voltage to the shoe of same signas on the web by adjusting the variable power supply 19. The appliedvoltage to neutralize normally is about the same or greater than thepotential on the web if the spacing is 1 mm or more between the shoe andthe web. The magnitude of the voltage applied depends upon the desiredcharge on the web, and can be varied as desired. Anywhere between voltsand as high as 10,000 or even 30,000 volts may be applied as needed.

The types of web materials that can be treated by the invention are manyand varied, such as cellulose triacetate film base or poly(ethyleneterephthalate) film base or other polyester film bases, which may or maynot have been coated with sensitized emulsions, subbing layers, orantihalation backing layers. 'Other webs can be formed of photographicpaper which may or may not have coatings of photosensitive emulsions,polyethylene or the like. Our novel method operates effectively when theweb material is electrically non-conductive, is in a dry condition, andis of constant thickness beforeand after passing between the roller 13and plate 15 (without a liquid or semi-liquid layer thereon).

The roller 13 can be an idler roller, with the web 11 being transportedby motor driven rollers located elsewhere.

Now referring to the embodiment shown in FIG. 2, the roller 13', thevariable power supply 19, the field meter and the voltage indicator 27,are all the same as described in connection with FIG. 1.

As shown in FIG. 2 a web 11' is passing straight through during aprocessing operation in contact with a series of rollers 13', 31 and 33,with each roller developing additional static charge on the web. Withoutusing the present invention this static charge can become so large as tocause serious sparking if the web is subsequently grounded. Suchsparking can have serious effects not only on the web itself but also onthe photographic film or paper which is exposed to the action of lightfrom the sparks. In order to counteract this, the meter 25 can be usedto measure the charge at a point past the rollers, and the voltage canthen be applied to the plate 15 to neutralize the static charge so as toprevent detrimental efiects.

To summarize, some of the improvements provided by the present inventionare: 7

Spark discharges are prevented when a web of photographic material isgrounded, thus avoiding spark damage to the sheet itself, and avoidingthe exposure of other photographic materials in the same darkroom.

The formation of detrimental islands of high charge density on a sheetof photographic film or paper base is prevented,

thus improving subsequent coating operations.

Accumulation of dust particles on a sheet of photographic material canbe prevented by reducing the static potential which tends to attract andhold dust particles.

The possibility of scratching a web or of depositing dirt particles, asmay occur with the prior art, is eliminated.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention. I

We claim:

1. In an apparatus for developing a predetermined electrical chargecondition on a transported flexible web, the combination comprising:

means for transporting a web in a transport system more conductingrollers; first electrically conductive means of said transport systemfor supporting one surface of the web;

second electrically conductive means spaced from said first conductivemeans and between which the web is transported by said web transportingmeans; I means for grounding one of said first and second conductivemeans;

adjustable means for applying a direct current voltage of a selectedmagnitude and sign to the other of said first and of one or secondconductive means for generating an electrostatic field withoutgenerating a corona discharge; 7 means adjacent said first and secondconductive means for monitoring the electrical charge on the web; and

means for adjusting said adjustable means in response to said monitoringmeans for generating a predetermined electrostatic field between saidfirst and second conductive means for developing'a predeterminedelectrical charge condition on the web.

2. The invention according to claim 1 wherein said first conductivemeans comprises a roller, and said second conductive means comprises anarcuate plate having a surface concentric with and spaced from saidroller.

3. The invention according to claim 1 wherein said first conductivemeans comprises a grounded roller, said second conductive meanscomprises an arcuate plate having a surface concentric with and spacedfrom said roller and electrically connected to said adjustable directcurrent voltage applying means, and said monitoring means is positionedto monitor the charge on the web after it leaves the roller.

' 4. A method of developing a predetermined electrical charge conditionon a flexible light-sensitive web material transported over a transportsystem of one or more conducting rollers, comprising the steps of:

transporting the web through opposed, spaced apart first and secondconductive members, one of which is grounded, and one of which isengaged by one side of the web;

monitoring the electrical charge on the web: and in response to themonitoring,

applying a direct current voltage of a selected magnitude and sign tothe ungrounded conductive member for generating a predeterminedelectrostatic field between said first and second conductive membersdeveloping a predetermined electrical charge condition on the web.

i ili i 1F

1. In an apparatus for developing a predetermined electrical chargecondition on a transported flexible web, the combination comprising:means for transporting a web in a transport system of one or moreconducting rollers; first electrically conductive means of saidtransport system for supporting one surface of the web; secondelectrically conductive means spaced from said first conductive meansand between which the web is transported by said web transporting means;means for grounding one of said first and second conductive means;adjustable means for applying a direct current voltage of a selectedmagnitude and sign to the other of said first and second conductivemeans for generating an electrostatic field without generating a coronadischarge; means adjacent said first and second conductive means formonitoring the electrical charge on the web; and means for adjustingsaid adjustable means in response to said monitoring means forgenerating a predetermined electrostatic field between said first andsecond conductive means for developing a predetermined electrical chargecondition on the web.
 2. The invention according to claim 1 wherein saidfirst conductive means comprises a roller, and said second conductivemeans comprises an arcuate plate having a surface concentric with andspaced from said roller.
 3. The invention according to claim 1 whereinsaid first conductive means comprises a grounded roller, said secondconductive means comprises an arcuate plate having a surface concentricwith and spaced from said roller and electrically connected to saidadjustable direct current voltage applying means, and said monitoringmeans is positioned to monitor the charge on the web after it leaves theroller.
 4. A method of developing a predetermined electrical chargecondition on a flexible light-sensitive web material transported over atransport system of one or more conducting rollers, comprising the stepsof: transporting the web through opposed, spaced apart first and secondconductive members, one of which is grounded, and one of which isengaged by one side of the web; monitoring the electrical charge on theweb; and in response to the monitoring, applying a direct currentvoltage of a selected magnitude and sign to the ungrounded conductivemember for generating a predetermined electrostatic field between saidfirst and second conductive members developing a predeterminedelectrical charge condition on the web.